With continuous development of display technologies, display panel manufacturing technology is also getting mature. Existing display panels mainly include organic light emitting diode (OLED) panels, liquid crystal display (LCD) panels, plasma display panels (PDP) and so on. An organic light emitting display device, as a self-luminous display device, does not require an independent light source. Thus, the organic light emitting display devices can operate at a low voltage, are lightweight and thin, and can provide high-quality characteristics such as a wide viewing angle, a high contrast and a quick response. Therefore, as a next generation of display devices, the organic light emitting display devices have attracted more attention. In addition, because of the characteristics of being lightweight and thin, the organic light emitting display panels are easier to fold, and thus are applied to the field of flexible display. However, the display effect of foldable display panels needs to be further improved.